High surface area alumina solid

ABSTRACT

An alumina solid is obtainable by a process comprising the step of contacting in a liquid medium at least one alumina precursor with at least one template comprising a membrane lipid or a mixture of two or more thereof.

The present invention relates to a high specific surface area aluminasolid, to a process for preparing it and to the use of membrane lipidsas templates.

The preparation of alumina solids is known per se. A survey of theprocesses currently in industrial use is given in Ullmann's Encycl.Tech. Chem. 5th Ed. 1997, pp. 561-562, and in Winnacker, Kuchler, 4thedition, Hanser-Verl. 1983 vol. 3, pp. 2-41.

Alumina thus prepared has a specific surface area in the range from 100to 400 m² /g and pore diameters of from 2 to 5 nm, with large-porealuminas generally having smaller surface areas. Such large-porealuminas have a broad pore size distribution up to 10 nm.

Mesoporous oxides have likewise been described, for example in DE-A 4407 326 and DE-A 195 43 638. According to these references, mesoporousoxides are prepared by adding a cationic, anionic or nonionic surfactantas a structure-directing reagent, or template, to the oxide precursors(monomers or oligomers) in the course of the polycondensation process togive an inorganic oxide. According to these references, the actualsynthesis is followed by thermal removal of the template surfactants,for example by calcining in air at from 350 to 600° C., giving rise to amesoporous, purely inorganic oxide.

"Mesoporous" means that the diameter of the pores in the solid is fromabout 2 to about 50 nm.

The pores of prior art mesoporous oxides are predominantly confined tothe range around 2 nm or so.

However, oxide solids which have larger pores and which are inexpensiveto produce are desirable for some applications, for example for use asheterogeneous catalysts, to optimize mass transfer in the reaction. Thisaim is achieved with some of the commercially available aluminas which,however, have broad pore diameter distributions and small specificsurface areas. Furthermore, heat treatment may lead to the formation ofvarious crystalline alumina phases (e.g. γ-Al₂ O₃ or, at even highertemperatures, α-Al₂ O₃) some of which have inherent catalytic propertiessuch as Lewis or Bronsted acidity and therefore have an undesirableeffect on the reaction to be catalyzed.

It is an object of the present invention to provide an alumina solidwhich is suitable for a multiplicity of applications, in particular foruse as catalyst or catalyst support, and a process for preparing thissolid in an economically favorable, i.e. inexpensive, way.

We have found that, surprisingly, this object is achieved by using amembrane lipid as template in the preparation of the alumina solid.

The present invention accordingly provides a process for preparing analumina solid, which comprises the step of contacting in a liquid mediumat least one alumina precursor with at least one template comprising amembrane lipid or a mixture of two or more thereof.

This invention further provides an alumina solid obtainable by a processcomprising the step of contacting in a liquid medium at least onealumina precursor with at least one template comprising a membrane lipidor a mixture of two or more thereof.

FIG. 1 shows the result of nitrogen adsorption on the solid ofExample 1. Here, p/p⁰ stands for the relative pressure, N₂ ^(ad) fornitrogen, adsorbed at the solid, + for measured values obtained duringadsorption, and ++ for measured values obtained during desorption.

FIG. 2 shows the X-ray diffraction pattern of the solid of Example 1.Here, I stands for the intensity of the registered signal in countunits.

FIGS. 2a and 2b show enlargements of details of this X-ray diffractionpattern.

"Template" refers to a substance which is initially mixed with thestarting materials and subsequently removed from the resulting solid,e.g. by thermal treatment, to leave the areas of the solid in which thetemplate was located in the form of pores.

As stated above, templates used according to the invention are membranelipids such as phospholipids, glycolipids and cholesterol. The term"membrane lipid" as used herein is defined as in L. Stryer--Biochemie,Spektrum der Wissenschaft Verlagsgesellschaft mbH, 1990, p. 296 andrefers to relatively small molecules which have a hydrophilic and ahydrophobic moiety and spontaneously form closed bimolecular layers inaqueous media. Such membrane lipids are described in detail in theabovementioned biochemistry textbook by L. Stryer on pp. 296ff.Furthermore, phospholipids in particular are described inRompp-Chemielexikon, 9th ed., vol. 4, pp. 3383/3384, ThiemeVerlag 1991,and in an article by Eibl in Angew. Chem. 96 (1984), p. 247-262, whichare all fully incorporated herein by reference for the membrane lipidsand phospholipids.

Examples of preferred membrane lipids are sphingolipids, i.e.phospholipids derived from sphingosine, phosphoglycerides, i.e.phospholipids derived from glycerol, e.g. phosphatidate, phosphatidylserine, phosphatidyl ethanolamine, phosphatidyl choline, phosphatidylinositol, diphosphatidyl glycerol, glycolipids, e.g. cerebroside andcholesterol.

However, phospholipids are preferred templates.

It is of course also possible to use as templates mixtures of two ormore membrane lipids, preferably mixtures of two or more of the membranelipids cited above.

The amount of membrane lipid used is generally not subject to anyparticular restrictions and is preferably from about 0.05 to about 50%by weight, more preferably from about 2 to about 10% by weight, in eachcase based on the synthesis batch, i.e. the total amount of aluminaprecursor, template and liquid medium.

Liquid media used in the process of the invention are preferably aqueoussolutions, for example mixtures of water and alcohols, e.g. ethanoland/or isopropanol. Contacting may also be carried out in water, anorganic solvent or a mixture of different organic solvents.

Preference is given to using alcohol solvents generated by hydrolysis ofthe alumina precursors, i.e., for example, ethanol when using aluminumethoxide (Al(OEt)₃), isopropanol when using aluminum isopropoxide andbutanol when using aluminum butoxide.

A usable alumina precursor is any compound which is converted to aluminaby calcining in air at elevated temperatures. The precursor may beemployed, for example, as an organometallic component, e.g. as alkoxide,Grignard compound, alkylate, chelate, e.g. with acetylacetonate, in aform which is soluble in an organic solvent, or in the form of solublesalts, as a hydroxide, as a colloid in an aqueous phase or as acombination of two or more thereof.

Contacting can be carried out at a basic, acidic or also at a neutralpH, preference being given to an acidic pH, especially a pH of from 1 to5.

After combining the alumina precursor and the template in a liquidmedium, the resulting suspension is brought to the appropriate pH andstirred at preferably from about -10° to 150° C., more preferably fromabout 10 to about 90° C., especially from about 20 to about 65° C., forabout 0.5 to about 72 hours, preferably from about 1 to about 48 hours,especially from about 10 to about 30 hours. When contacting thecomponents described above, the pressure is preferably from about 0.4 toabout 300 bar, more preferably from about 0.8 to about 150 bar andespecially from about 1 to about 10 bar.

The resulting suspension is then separated from the liquid medium, forexample by centrifugation or simple filtration, and subsequently dried.Drying is preferably effected initially at ambient temperature for fromabout 5 to about 72 hours, preferably from about 10 to about 48 hours,especially from about 20 to about 30 hours, and then at an elevatedtemperature in the range of from about 50 to about 100° C., preferablyfrom about 55 to about 70° C., for several hours.

The alumina solid dried in this manner is subsequently calcined at fromabout 350 to about 800° C., preferably from about 400 to about 700° C.,especially from about 450 to about 600° C., for from about 2 to about 10hours, preferably from about 4 to about 6 hours, in the presence ofoxygen, preferably in air.

During the contacting of the alumina precursor with the template, thefollowing additional components may be added:

pharmacologically active organic or inorganic compounds such asanalgesics or cardiovascular agents, in which case the incorporation ofthese compounds into the alumina solid results in retarded release ofthe pharmacologically active compound on application;

enzymes for biotechnological application such as oxidases, reductases,transferases, hydrolases, lyases, isomerases, ligases and semi-syntheticand synthetic enzymes as described, for example, in Science, 223 (1984)p. 165ff, Cold Spring Harbor Symp. Quant.Biol. 52 (1987), I. 75-81, andTetrahedron 40 (1994), p. 269-292, the relevant contents of which arefully incorporated herein by reference;

pigments such as ferromagnetic pigments, e.g. chromium(IV) dioxide,ferrites, iron oxides, iron or iron alloys, further inorganic pigments,e.g. chalk, graphite, titanium white, white lead or zinc white, carbonblack, luminescent pigments, e.g. zinc sulfide or alkaline earth metalaluminates, organic pigments such as azo pigments, indigoid pigments,phthalocyanine pigments, metal complex pigments or diketopyrrolopyrrolepigments, which are likewise present in encapsulated form in theresulting alumina solid.

In the preparation of the alumina solid of the invention, it is alsopossible to add, in particular via the aqueous phase, an ionic compoundof an element of main groups I to III except aluminum or of transitiongroups I to VIII of the Periodic Table of the Elements, the lanthanoids,silicon, germanium, tin, lead, phosphorus, antimony, bismuth, sulfur,selenium, tellurium or a mixture of two or more thereof, preferablysodium, potassium, calcium, magnesium, beryllium, boron, gallium,indium, silicon, germanium, tin, lead, antimony, bismuth, scandium,yttrium, lanthanum, titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron,cobalt, nickel, ruthenium, copper, zinc, cadmium, mercury, cerium,europium, thorium, uranium or a mixture of two or more thereof, morepreferably sodium, potassium, calcium, magnesium, beryllium, boron,gallium, indium, silicon, germanium, tin, lead, bismuth, titanium,zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,tungsten, manganese, rhenium, iron, cobalt, nickel, ruthenium, copper,zinc, cadmium, mercury, cerium or a mixture of two or more thereof.

The elements cited above may be employed especially in the form of theirsulfates, phosphates, nitrates, carbonates, halides and perchlorates andalso in the form of easily hydrolyzable organometallic compounds such asalcoholates, chelates, carboxylates, preferably in the form of sulfates,phosphates and nitrates, more preferably in the form of sulfates andnitrates.

They can also be employed in the form of isopoly cations or heteropolycations as described in references DE-A 44 07 326 and DE-A 195 43 638which were mentioned at the beginning and the relevant contents of whichare likewise fully incorporated herein by reference.

In a further embodiment of the present invention, the mixture of aluminaprecursor, template and liquid medium may be applied to an inert poroussupport, for example a porous glass, a silica gel, diatomaceous earth orclay, a ceramic material, a metal, a metal packing or a metal mesh asused for static mixers or reactive distillation column packings, forexample. This makes it possible to produce inert supports covered orimpregnated with alumina solid by the process of the invention toprovide composite materials which have improved mechanical stability andimproved permeability in the catalytic reactor compared to the startingmaterials.

In this context, metallic support materials, for example the stainlesssteels having the material numbers 1.4767, 1.4401, 2.4610, 1.4765,1.4847, 1.4301, etc., are particulary useful since their surface can beroughened by heat treatment before they are covered/impregnated with thesolids. Particular preference is given to using Kantahl (material number1.4767) or alumina-containing metals as mesh material. Kantahl is analloy containing about 75% by weight of Fe, about 20% by weight of Crand about 5% by weight of Al. Heat treatment is effected by heating themetallic supports cited above in air at temperatures of from 600 to1100° C., preferably from 800 to 1000° C., for from one to twenty hours,preferably from one to ten hours, and cooling back down. Thispretreatment is described in EP-A-0 564 830 and important since the heattreatment significantly improves the bonding between the solids and themetallic supports.

If contacting is effected at a stationary interface, i.e. at theinterface of two immiscible fluids, the alumina solid may be obtained inthe form of thin films or layers since the presence of such an interfacemakes it possible to provide the solid, during its preparation, with aparticular oriented structure such as a thin film. Further details aredescribed in DE-A 19624862.0. Thin films or layers obtained in thismanner may be employed in membrane, separation or purification processesor may be used for information storage. Such applications are described,for example, in DE-A 44 24 221, the relevant contents of which are fullyincorporated herein by reference.

Such solids may be utilized in particular for electronic, optical orelectro-optic applications; corresponding membranes are utilized in thecatalytic conversion in membrane reactors or in reactive distillations.The present invention accordingly also provides for the use of a solidof the invention as catalyst or catalyst support, as matrix for activecomponents, in membrane, separation or purification processes, forproducing electrical, optical or electro-optic components such asswitching devices or sensors, for producing oxide ceramics or forseparating substances, as adsorbent, as filler, especially in polymers,as fire retardant and as abrasives and polishing materials.

If the solid of the invention is used as catalyst or catalyst support,it is particularly useful in hydrocarbon oxyfunctionalization, olefinoxidation to give oxiranes, aromatics alkylation, hydrogenation,dehydrogenation, hydration, dehydration, isomerization, an additionreaction, an elimination reaction, nucleophilic or electrophilicsubstitution, dehydrocyclization, hydroxylation of heteroaromaticcompounds, aromatics hydroxylation, epoxy-aldehyde rearrangement,amination of monomeric or oligomeric olefins, an aldol type condensationreaction, a polymerization reaction, an esterification oretherification, the catalytic conversion of exhaust gases and flue gasesand for nitrogen oxide removal.

The solid of the invention is in particular characterized by thefollowing properties:

In X-ray analysis, its strongest reflections are in the angular range ofless than 4° (2 θ) when measured using Cu K.sub.α radiation.

The solid has pores in the range from about 2 to about 50 nm, preferablyfrom about 4 to about 30 nm, especially from about 6 to about 10 nm, thepore diameter being determined by nitrogen adsorption at 77 K. Thespecific surface area determined under the same conditions as evaluatedby the method of Barret, Joyner and Halenda according to J. Am. Chem.Soc., 73 (1951), 373-380, is more than about 100 m² /g, preferably morethan about 250 m² /g, especially from about 300 to 550 m² /g.

The pore volume, likewise determined by nitrogen adsorption at 77 K, ismore than about 0.2 ml/g, preferably more than about 0.25 ml/g,especially from about 0.5 ml/g to 1.0 ml/g.

The present invention further provides the use of a membrane lipid or amixture of two or more thereof as templates in the preparation of analumina solid.

The Examples which follow illustrate the preparation and the propertiesof the solid of the invention and relate it to a Comparative Exampleprepared according to a prior art method, i.e. without adding a membranelipid.

EXAMPLES Example 1

A solution of 205.8 g of aluminum triisopropoxide (Merck), 300 g ofethanol and 81.0 g isopropanol was homogenized for 30 minutes in a 2 lfour-neck flask. 50.0 g of soybean lecithin PC 40-45 comprising 40-45%phosphatidyl choline, 10% phosphatidyl ethanolamine and 2% phosphatidylinositol (Gienow, Pinneberg) were then added to this mixture. Uponaddition of a solution of 650.0 g of deionized water and 7.5 g ofhydrochloric acid solution (10% by weight) a suspension was formed. Thesuspension was stirred at room temperature for 24 h, filtered and driedin air for 24 h. The solid was then dried at 60° C. overnight. 124 g ofsolid were obtained. The solid was finally calcined in air at 500° C.for 5 hours. The loss on calcination was 113% by weight, based on thesolid used.

Nitrogen adsorption at 77 K gave a typical hysteresis in the relativepressure range p/p^(o) >0.6 as shown in FIG. 1. Application of the BJHmodel to these results gave a pore surface area of 497 m² /g for poresin the range from 6 to 7 nm. The corresponding pore volume was 0.81 ml/gas determined at a relative pressure p/p^(o) of 0.98. The most frequentpore diameter was about 7 nm.

X-ray analysis of the solid obtained in this manner gave the highestreflection intensities at angles of less than 4° (2 θ) (Cu K.sub.αradiation). The diffraction pattern is shown in FIGS. 2, 2a and 2b.

Comparative Example 1

A solution of 205.8 g of aluminum triisopropoxide (Merck), 300 g ofethanol and 51.0 g of isopropanol was homogenized for 30 minutes in a 2l four-neck flask. Upon addition of a solution of 650.0 g of water and7.5 g of the hydrochloric acid solution (10% by weight) a whitesuspension was formed. The white suspension was stirred at roomtemperature for 24 h, filtered and dried at room temperature in air for24 h and then at 60° C. overnight. 87.7 g of solid were obtained. Thesolid was finally calcined at 500° C. for 5 hours. The loss oncalcination was 28.2% by weight.

X-ray analysis of the solid obtained in this manner gave no distinctreflections at angles of less than 4° (2 θ). The solid was pure γ-Al₂O₃.

Nitrogen adsorption at 77 K gave typical hystereses in the relativepressure range p/p^(o) >0.4. Application of the BJH model to theseresults gave pore sizes in the range from 2 to 5 nm. The pore surfacearea according to the BET method was 289 m² /g. The corresponding porevolume was only 0.37 ml/g as determined at a relative pressure p/p^(o)of 0.98. The most frequent pore diameter was about 3.8 nm.

We claim:
 1. In a process for preparing a porous alumina, wherein atleast one organoaluminum component is hydrolyzed in a liquid aqueousmedium, the improvement which comprises conducting the hydrolyzation inthe presence of at least one template comprising a membrane lipidselected from the group consisting of sphingolipids, phospholipidsderived from sphingosine, phosphoglycerides, phospholipids derived fromglycerol, phosphatidate, phosphatidyl serine, phosphatidyl ethanolamine,phosphatidyl choline, phosphatidyl inosidol, diphosphatidyl glycerol,glycolipids, cerebroside, and cholesterol.
 2. A process as defined inclaim 1, wherein the liquid aqueous medium is a mixture of water andalcohol.
 3. A process as defined in claim 1, wherein the organoaluminumcomponent is selected from the group consisting of alkoxide and Grinardcompound, alkylate, chelate.
 4. A process as defined in claim 1, whereinthe membrane lipid is a phospholipid or a mixture of two or morethereof.
 5. A process as defined in claim 1, wherein the hydrolyzing isconducted in the presence of at least one element selected from thegroup consisting of sodium, potassium, calcium, magnesium, beryllium,boron, gallium, indium, silicon, germanium, tin, lead, bismuth,titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, manganese, rhenium, iron, cobalt, nickel,ruthenium, copper, zinc, cadmium, mercury and cerium.
 6. A process asdefined in claim 1, wherein the hydrolyzing is conducted in the presenceof a pharmacologically active organic or inorganic compound, an enzyme,a pigment or a mixture of two or more thereof.
 7. A process as definedin claim 1, wherein the hydrolyzing is carried out in the presence of aninert porous support.